Surface gravity wave effects on the upper ocean boundary layer: Modification of a one-dimensional vertical mixing model

The impact of ocean surface gravity waves on the near-surface currents and on the upper ocean mixed layer is investigated using the one-dimensional general ocean turbulence model (GOTM). The goal of the investigation is to determine coupling methodology which required theories, modifications and parameterizations to incorporate the influence of surface wave forcing into an ocean dynamic model. To this end, some well-known theories of air–sea interaction are applied to modify momentum and energy equations to include the surface wave stress, wind energy input, wave dissipation, and Stokes drift. A two dimensional wave energy spectrum is used as a representative sea state for a sufficiently large fetch. The performance of the wave-modified model is tested by a series of model experiments which cover a number of features of the upper ocean boundary layer on diurnal and seasonal time scales. These sets of model experiments include both some idealized test cases to show the importance and sensitivity of the upper ocean to wave parameterizations, and some additional observation-oriented experiments which highlight the role of the modifications in improving the prediction of the upper ocean dynamical variability. The results confirm again the dominant role of Stokes drift in influencing both the magnitude and the angular turning of the surface Ekman current and the evolution of the upper ocean boundary layer (mixed layer depth and temperature evolution), in comparison with other wave induced parameters. Meanwhile, it is shown that the modified model is sensitive to wave parameterizations and the wave energy spectrum. However, there remain a number of uncertainties due to choice of wave energy spectrum, wave forcing parameterization, the surface eddy viscosity, momentum and energy surface boundary conditions, and the role of some important processes excluded from this study, such as the effect of Langmuir circulations.